This proposal is concerned with both the activation of specific genes and the role of these genes in the formation of specific cellular structures in a metazoan, and can provide significant contributions to two basic areas of biological investigation: (1) cellular differentiation and (2) spermatogenesis and spermatozoan motility. The system being studied is spermatid differentiation in Drosophila melanogaster. By combining genetic, ultrastructural, and biochemical approaches we intend to correlate specific gene activity with specific developmental events during spermiogenesis. Attention is being focused on the special nature and role of the Y chromosome in this process. A major goal of this laboratory is an understanding of the genetic organization, function, and regulation of this chromosome; and the role of this chromosome in regulating the activities of X and autosomal genes. Additionally the role and regulation of ribosome biogenesis during spermiogenesis will be pursued in rDNA deficient males. The methods of investigation include testes isolation and fractionation, electron microscopy, autoradiography, electrophoresis, density gradient centrifugation, and molecular hybridization.